The present invention relates to a gas, that is, a cleaning or etching gas, for removing deposits by a gas-solid reaction and a removal method using the gas.
In thin-film device production process of semiconductor industry, optical device production process, super steel material production process and the like, various thin films, thick films, powders, whiskers and the like are produced, for example, by chemical vapor deposition, (CVD), physical vapor deposition (PVD), sputtering, and sol-gel process. During the production of these materials, unnecessary deposits in the form of film, whisker or powder are inevitably formed, for example, on a reactor""s inner wall and a jig for supporting the object, as well as on the object. This may cause the occurrence of unnecessary particles, making it difficult to produce films, powders, whiskers and the like of good quality. Thus, it becomes necessary to occasionally remove the unnecessary deposits, for example, by cleaning gas. Such a cleaning gas is required, for example, to have (1) a high reaction rate at which the cleaning gas reacts with unnecessary deposits to form volatile compounds, (2) a relative easiness to make the exhaust gas of the cleaning unharmful, and (3) a relative unstableness in the atmosphere to make the impact on the global warming smaller. Conventional examples of the cleaning gas are C2F6, CF4, C4F8, NF3 and ClF3. These compounds, however, have the following defects. Firstly, ClF3 is highly reactive, and thus may do damage to materials conventionally used for the apparatus, when ClF3 is used at a high temperature or with the assistance of plasma. Secondly, NF3 is low in reactivity unless the reaction temperature is at least 300xc2x0 C., and thus may be impossible to remove unnecessary deposits accumulated in the piping of the apparatus and the outside of the plasma region. Furthermore, it is necessary to have a high temperature in order to make the exhaust gas unharmful. Thus, the cost for conducting the cleaning becomes relatively high. Thirdly, each of C2F6, CF4 and C4F8 has the following defects. That is, it may be impossible to remove unnecessary deposits accumulated in the piping of the apparatus and the outside of the plasma region. Furthermore, a fluorocarbon(s) will accumulate by the plasma cleaning. If oxygen is added in order to decrease the amount of the accumulation of the fluorocarbon(s), an oxide(s) will accumulate instead. Since each of C2F6, CF4 and C4F8 is a very stable compound, it is difficult to treat the exhaust gas of the cleaning. In other words, these compounds (gases) will be stably present in the environment, and cause adverse impact against the environment due to their high global warming coefficients or factors. Thus, it is necessary to have a high temperature for the treatment of the exhaust gas. This makes the cost of the treatment relatively high.
An etching gas, which is analogous to the above-mentioned cleaning gas, is used for partially removing a thin film material in order to transfer the circuit pattern, for example, of LSI and TFT. Conventional examples of this etching gas are CF4, C2F6, CHF3, SF6, and NF3. These gases have a problem of high global warming coefficient. Furthermore, these gases are relatively stable gases. Thus, it is necessary to use a large amount of energy for generating, for example, CF3 radicals and F radicals, which are useful as etchant. That is, the electric power consumption becomes large. Furthermore, it is relatively difficult to treat the unreacted etching gases, prior to the discharge into the atmosphere. Therefore, there is an urgent demand for an alternative etching gas(es) that can easily be made unharmful on the global environment and is capable of achieving high precision etching.
It is therefore an object of the present invention to provide a gas for removing deposits, which gas can easily be made unharmful on the global environment after the removal of deposits.
It is a more specific object of the present invention to provide a cleaning gas for efficiently removing unnecessary deposits accumulated, for example, in an apparatus for producing semiconductor devices, which cleaning gas can easily be made unharmful on the global environment after the removal of the deposits.
It is another specific object of the present invention to provide an etching gas for removing, as precisely as originally designed, an unwanted portion of a film deposited on a substrate, for example, for producing thin film devices (e.g., LSI and TFT), which etching gas can easily be made unharmful on the global environment after the removal of the unwanted portion.
It is a still another object of the present invention to provide a method for removing a deposit by the gas.
According to the present invention, there is provided a gas for removing deposits by a gas-solid reaction. This gas comprises a hypofluorite that is defined as being a compound having at least one OF group in the molecule. We unexpectedly found that various deposits can be removed by the gas and that the gas can easily be made unharmful on the global environment after the removal of the deposits. The gas may be a cleaning gas for substantially completely removing the deposits. In other words, this cleaning gas is used for cleaning, for example, the inside of an apparatus for producing semiconductor devices. This cleaning gas comprises 1-100 volume % of the hypofluorite. We unexpectedly found that various unnecessary deposits can efficiently be removed by the cleaning gas. Furthermore, either of plasma-assisted and plasma-less cleanings is made possible by the cleaning gas. Alternatively, the gas according to the present invention may be an etching gas for removing an unwanted portion of a film deposited on a substrate. In other words, the etching gas is used, for example, in pattern transfer operations in the production of semiconductor circuits. We unexpectedly found that the unwanted portion can be removed by the etching gas as precisely as originally designed.
According to the present invention, there is provided a method for removing a deposit by the gas. This method comprises the step (a) bringing the gas into contact with the deposit, thereby to remove the deposit by a gas-solid reaction. The above-mentioned unexpected findings are also obtained by this method.